GB906398A - Stitch-forming mechanism for lock stitch sewing machines - Google Patents

Abstract

906,398. Sewing-machines. SINGER MANUFACTURING CO. March 6, 1961 [March 18, 1960], No. 7996/61. Class 112. A lock-stitch looptaker comprises a rotary bobbin journalled therein, means for imposing friction on thread passing therethrough, means for introducing one limb of a thread loop engaged by the loop-seizing beak to the friction means, and means for drawing said limb through the friction means and for winding the thread drawn through the friction means upon the bobbin. The looptaker is the rotary hook incorporated in the single-thread, clamp-feed, group-stitch machine described in Specification 906,397. The rotary portion comprises a body 83 fixed by a screw 82 to a hollow driving-shaft 31 and formed with a looptaking beak 85, a gib 160, and a tubular member 166 formed with a circumferential thread-camming edge 167. A stationary bobbin case 120 is formed with a circumferential flange 130 journalled between body 83 and gib 160, and with a notch 132 engaged loosely by a fixed lug 133. A bobbin 121, journalled on a hub 123 within the bobbin case and held in position by a screw 124, has a thread-accommodating spindle 125 disposed between flanges 126, 126<1>. Fixed to body 83 opposite a gap 84 therein is a leaf-spring 92 which is also disposed adjacent the beak 85. A shaft 104, slidable within shaft 31, carries at its end a cylindrical, bobbin-winding member 101 which is formed with a radial lug 102 slidably disposed within gap 84. A leaf-spring 111, secured to the rear face of member 101, carries a pin 113 which passes through an aperture 114 in member 101. When shaft 104 is moved inwardly, lug 102 presses spring 92 against beak 85, member 101 abuts the inner face of the bobbin 121, and pin 113 enters one of three recesses 129 formed in bobbin 120 to couple the latter to the bobbin-driving shaft 31. Flange 130 is formed with a gap having ends 140, 141, respectively. A slot 142 extends axially in the bobbin case at end 140 and enters a circumferential slot 143. A leaf-spring 150, disposed in slot 143, is biased against the inner wall of the latter by screws 151, 152, and is formed with an external lug 153. The bobbin case is formed with a needle-passing slot 144 adjacent end 140. The arrangement is such that at the commencement of a serving operation the thread tension is released, no work feed occurs, and shaft 104 is moved inwardly. The thread loop taken by beak 85 is thereby clamped to it by spring 92, actuated by lug 102, and the bobbin 121 rotates with shaft 31. The thread limb extending from the needle 26 to beak 85 cannot pass from end 140 to end 141 owing to the proximity of member 101, but instead enters slot 142 and is drawn by the action of camming edge 167 along slot 142 and then between spring 150 and the inner wall of slot 143, till it is arrested by lug 153. On further rotation of the looptaker beak, said limb is drawn past spring 150 over flange 126 and is progressively wound upon the spindle 125. When shaft 104 is moved outwardly to uncouple the bobbin and to unclamp the thread from beak 85, spring 92 continues to impose a degree of frictional resistance to the passage of the thread over beak 85, whereby the loose end of thread extending from the beak is drawn over flange 126 and is wrapped on spindle 125.